System and method for processing audio data for narrow geometry speakers

ABSTRACT

In one representative embodiment, one or several mono audio signals and corresponding positional information are processed by respective mixing blocks. The positional information may include azimuth information, elevation information, and range information. For each mono audio signal, a plurality of left and right signals are generated using mixing techniques. The corresponding left and right signals from the plurality of mixing blocks are combined resulting in a single set of left and right signals These signals are then processed with the various placement filters and the outputs of the placement filters are combined to generate a stereo signal for output using narrow geometry speakers.

FIELD OF THE INVENTION

The present application is generally related to processing audio data toprovide a three dimensional effect.

DESCRIPTION OF RELATED ART

A number of audio processing algorithms exist that enable a listener toperceive that an audio signal is originating from a defined location inthree dimensional space using just two speakers. The first significantreproductive system was developed by Schroeder and Atal in 1963. Thissystem relied on the concept of cross talk cancellation. Like stereoreproductive systems, three dimensional reproductive systems based oncross talk cancellation require that the listener be positioned in a“sweet spot.” This area is the apex of an equilateral triangle formed bythe speakers and the listener. The speakers are therefore placed atazimuth angles of 30 degree to the listener. Since Schroeder and Atal,there have been some alternative approaches. One in particular, was thatachieved by Lowe and Lees, who took a purely empirical approach andconstructed transaural transfer functions, based on frequency dependantphase and amplitude shifts. This approach produced very effective andefficient transfer functions.

SUMMARY

These technologies enable a number of useful effects. However, thesetechnologies exhibit the desired performance only when speakers arerelatively widely spaced (more than eight inches of separation). Anumber of devices are becoming available that do not allow multiplespeakers to be sufficiently spaced. When a three dimensional positioningalgorithm is incorporated within such a device, cancellation between thespeakers becomes more significant due to the narrow configuration of thespeakers. Accordingly, a significant amount of amplitude attenuationoccurs. Additionally, a significant amount of frequency content is lost.In many cases, the audio experience is reduced to unacceptable levels bysuch technologies when narrow speaker geometries are employed.

Accordingly, it is an object of the present invention to provide amethod and apparatus for reproducing three dimensional audio using astereo playback system with narrowly spaced speakers.

A further object of the present invention is to provide a method andapparatus for reproducing three dimensional audio using a stereoplayback system with narrowly spaced speakers in which a pre-processoris provided that accepts mono audio data and its respective positionalinformation as inputs, processes such inputs and outputs multiple stereostreams to a filtering processor apparatus.

According to an aspect of the present invention, both processing blocksare provided for insertion between a signal source and the final poweramplifier stage. The above and other objects, features, and advantagesof the present invention will become apparent from the followingdetailed description of illustrative embodiments thereof to be read inconjunction with the accompanying drawings, in which like referencenumerals represent the same or similar elements. The advantage of thisapproach is that the integrity of the information between the speakersis maintained.

Representative embodiments combine the benefits of the aforementionedinventions for localizing sound and for stereo enhancement thus enablingthree dimensional effects to be experienced by users of devices thatpossess narrow geometry speaker designs (designs having speakers spacedapart by eight inches or less). In one representative embodiment, one orseveral mono audio signals and corresponding positional information areprocessed by respective mixing blocks. The positional information mayinclude azimuth information, elevation information, and rangeinformation. For each mono audio signal, a plurality of left and rightsignals are generated using panning techniques. The corresponding leftand right signals from the plurality of mixing blocks are summedresulting in a single set of left and right signals. The signals withinthis set are processed by respective placement filters. The summedoutputs of these placement filters are combined to generate a stereosignal for output using narrow geometry speakers.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated that the conception and specific embodimentdisclosed may be readily utilized as a basis for modifying or designingother structures for carrying out the same purposes of the presentinvention. It should also be realized that such equivalent constructionsdo not depart from the invention as set forth in the appended claims.The novel features which are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and advantages will be better understood from thefollowing description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a three dimensional localization block for processingmono audio information and positional information according to onerepresentative embodiment.

FIG. 2 depicts a more detailed view of a three dimensional localizationblock for processing mono audio information and positional informationaccording to one representative embodiment.

FIG. 3 depicts a more detailed view of another three dimensionallocalization block for processing mono audio information and positionalinformation according to one representative embodiment.

FIG. 4 depicts an implementation of an azimuth placement filteraccording to one representative embodiment.

FIG. 5 depicts a flowchart according to one representative embodiment.

FIG. 6 depicts a portable device having a narrow speaker geometry andemploying audio processing according to one representative embodiment.

DETAILED DESCRIPTION

Referring to the drawings, FIG. 1 depicts three dimensional localizationblock 100 that provides a three dimensional effect to audio signalsaccording to one representative embodiment. Block 100 processes one orseveral mono audio channels (shown as inputs 1-N) and associatedpositional information. The positional information may include azimuthinformation, elevation information, and range information. Using thepositional information, the mono audio signals are preferably processedto generate azimuth left, azimuth right, above left, above right, belowleft, and below right signals. These signals are then processed withinblock 100 using placement filters to localize the audio field. Also, theazimuth filter retains center information (i.e., the placement filterretains a greater amount of energy) and is advantageous for narrowspeaker geometries. The other channels are preferably processed byrespective filters that “position” the signals to provide a perceptionof the directionality of the respective signal (e.g., below left). Theoutputs of the various filters are combined and outputted to left andright speakers.

FIG. 2 depicts system 200 where a single mono input signal is processedto receive a three dimensional effect according to one representativeembodiment. As previously shown, the mono audio signal is received withpositional information. Using the positional information, mixing block220 processes the mono input audio signal using panning techniques togenerate respective signals intended for left and right speakers. Forexample, if the positional information indicates that a sound originatedfrom the extreme right of the listener, a respective “right” signalwould be generated to possess substantially greater amplitude that therespective “left” signal. If the positional information indicates that asound originated from immediately in front of the listener, therespective right and left signals would possess approximately equalamplitude. For positions between the two extremes, various amplituderatios may be employed according to known panning algorithms.

Separate processing preferably is applied for azimuth and elevationinformation whereas ranging position is implemented through volumescaling in the mixer. The generated signals may include azimuth leftsignal 201, azimuth right signal 202, above left signal 203, above rightsignal 204, below left signal 205, and below right signal 206. Azimuthleft signal 201 and azimuth right signal 202 are preferably generatedusing azimuth information. Above left signal 203 and above right signal204 are preferably generated in response to elevation information.Likewise, below left signal 205 and below right signal 206 are similarlygenerated. Range information may be used to selectively scale thevarious signals.

Each left and right signal is then provided to filter processing block240. Within filter processing block 240, filter 207 processes azimuthsignal 201 and azimuth signal 202. Filter 207 may be implemented usingthe design shown in FIG. 4. Azimuth filter 207 removes a portion of theaudio information (“center” information) that is common or substantiallycommon to both the left and right signals before processing the signalin left and right sound placement filters. The outputs of the processingblock 207 provide azimuth positioning. Placement filters 208-211 processthe remaining signals. Filters 208-211 may be implemented using finiteimpulse response (FIR) designs with delay, infinite impulse response(IIR) responses, and other suitable designs. The respective rightsignals are combined using adders 212 and 213. The respective leftsignals are combined using adders 214 and 215.

The combined signals are then provided to left and right speakers (notshown) and the listener experiences a three dimensional effect in theaudio experience. Additionally, because the placement filter retainscenter information, relatively little amplitude attenuation occurs.Accordingly, the output signals of system 100 may be provided tospeakers having narrow speaker geometries.

FIG. 3 depicts system 300 where multiple mono input signals areprocessed to receive a three dimensional effect according to onerepresentative embodiment. System 300 operates in a manner that issubstantially similar to the operations of system 200. Each mono inputsignal with positional information is provided to a respective mixingblock 220 that processes the signals using panning techniques. In onepreferred embodiment, the corresponding signals from mixing blocks 220are then combined in a cascaded manner using adders 301. After all ofthe corresponding signals have been combined, a single filter processingblock 240 filters the signals and outputs a left and right signal forprovision to speakers.

FIG. 4 depicts an implementation of placement filter 400 according toone representative embodiment. Left and right signals are received andscaled by elements 401 and 402. The left scaled signal is then providedto multiplier 403 and highpass filter 407. Similarly, the right scaledsignal is provided to multiplier 404 and highpass filter 408. Element405 subtracts the signal from multiplier 404 from the signal fromhighpass filter 407. Likewise, element 406 subtracts the signal frommultiplier 403 from the signal from highpass filter 408. Thereby, theinformation that is substantially common to the right and left channelsis removed. The respective difference signals are respectively processedby multipliers 409 and 410, placement filters 411 and 412, and delayelements 413 and 414.

Referring again to the scaled versions of the original left and rightchannels, further scaling is preferably performed by multipliers 415 and416 and delay is provided by delay elements 417 and 418. The outputs ofdelay elements 417 and 418 are respectively combined using adders 419and 420. At this point, the center information is added to the signalsgenerated by placement filters 411 and 412. Specifically, the outputs ofadders 419 and 420 are signals that possess azimuth information whileretaining center information.

Additional details regarding the implementation of this placementprocessing may be found in U.S. Pat. No. 5,440,638 which is incorporatedherein by reference.

FIG. 5 depicts a flowchart according to one representative embodiment.In step 501, one or several mono audio signals are received withcorresponding positional information. In step 502, each of the monoaudio signals is processed to generate a plurality of signals usingpanning techniques. In step 503, selected ones of the correspondingsignals are combined (if multiple mono audio signals are received). Instep 504, the signals are processed using an azimuth filter and aplurality of placement filters. In step 505, the outputs of the azimuthfilter and the placement filters are combined to generate a single rightsignal and a single left signal. In step 506, the single right signaland single left signal are provided to speakers having a narrow speakergeometry.

FIG. 6 depicts portable device 600 (e.g., a cellular phone) includingentertainment functionality suitable for use in conjunction with somerepresentative embodiments. Device 600 includes speakers 601-1 and 601-2that are relatively closely spaced (e.g., within eight inches orapproximately within 20 cms). Accordingly, the use of existingtechnologies by device 600 would result in an unacceptable audioexperience. Accordingly, device 600 provides a three dimensional effectto audio signals using the processing previously described herein.

In one representative embodiment, the three dimensional effectprocessing is achieved using processor 602 and audio software 604. Whena user selects a respective application 603 (e.g., a video game), theapplication 603 may provide one or several mono audio signals to audiosoftware 604 with positional information, audio software 604 provides athree dimensional effect to each mono audio signal by processing withrespective mixing blocks, combining corresponding signals from themixing blocks, and filtering the corresponding signals. Althoughsoftware is used in one representative embodiment, integrated circuitrymay be used in lieu thereof and in addition if desired.

Due to the combination of processing, the listener experiences a degreeof directionality in the listening experience. Moreover, the centerinformation is retained and the amplitude of the stereo signals havingthe three dimensional effects is maintained and low frequency content isretained. Accordingly, the listening experience is maintained at arelatively high level even when narrow speaker geometries are employed.Additionally, the complexity of the audio processing is maintained atreasonable levels for multiple audio signals and, hence, the processingis suitable for a wide range of devices and applications.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the invention asdefined by the appended claims. Moreover, the scope of the presentapplication is not intended to be limited to the particular embodimentsof the process, machine, manufacture, composition of matter, means,methods and steps described in the specification. As one will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized. Accordingly, the appended claims areintended to include within their scope such processes, machines,manufacture, compositions of matter, means, methods, or steps.

1. A method comprising: receiving a mono audio signal and positionalinformation; generating a plurality of signals from said mono audiosignal using said positional information according to a panningalgorithm; processing a left signal and a right signal of said pluralityof signals by an azimuth filter, wherein said azimuth filter removesaudio information that is substantially common to said left signal andright signal before filtering by left and right placement filters andcombines outputs of said left and right placement filters with saidremoved audio information; processing remaining signals of saidplurality of signals using respective placement filters; combiningsignals generated by said processing a left signal and a right signaland signals generated by processing said remaining signals to produce astereo signal; and providing said stereo signal for output using twospeakers having a narrow geometry.
 2. The method of claim 1 wherein saidgenerating a plurality of signals generates an azimuth left signal, anazimuth right signal, a below left signal, a below right signal, anabove left signal, and an above right signal.
 3. The method of claim 1wherein said positional information includes azimuth information andelevation information.
 4. The method of claim 3 wherein said positionalinformation further includes range information.
 5. The method of claim 1wherein said two speakers are integrated in a handheld device.
 6. Asystem comprising: a mixing block for receiving a mono audio signal andpositional information, wherein said mixing block is operable togenerate a plurality of left and right signals using said positionalinformation according to a panning algorithm; a filter block forfiltering said plurality of left and right signals from said mixingblock, wherein said filter block comprises (i) an azimuth filter thatremoves audio information that is substantially common to said leftsignal and right signal before filtering by left and right placementfilters and combines outputs of said left and right placement filterswith said removed audio information, (ii) said filter block furthercomprises a plurality of placement filters for filtering remainingsignals of said plurality of left and right signals, and (iii) aplurality of adders for combing left and right signals from saidexpanding filter and said placement filters; and speakers having anarrow geometry for rendering output signals from said filter block. 7.The system of claim 6 wherein said system comprises a plurality ofmixing blocks and a plurality of adders for combining correspondingsignals from said plurality of mixing blocks before filtering by saidfilter block.
 8. The method of claim 6 wherein said mixing blockgenerates an azimuth left signal, an azimuth right signal, a below leftsignal, a below right signal, an above left signal, and an above rightsignal.
 9. The method of claim 6 wherein said positional informationincludes azimuth information and elevation information.
 10. The methodof claim 9 wherein said positional information further includes rangeinformation.
 11. The method of claim 6 wherein said system is a handhelddevice.
 12. A method comprising: receiving a plurality of mono audiosignals and associated positional information; generating a respectiveset of signals from each of said plurality of mono audio signals usingsaid associated positional information according to a panning algorithm;combining azimuth left signals and azimuth right signals from each ofsaid sets; combining above left signals and above right signals fromeach of said sets; combining below left signals and below right signalsfrom each of said sets; processing said combined azimuth left signal andcombined right signal by an azimuth filter, wherein said azimuth filterremoves audio information that is substantially common to said combinedazimuth left signal and said combined azimuth right signal beforefiltering by placement filters, and combines outputs of said placementfilters with said removed audio information; processing said combinedabove left signal, said combined above right signal, said combined belowleft signal, and said combined right signal by respective placementfilters; combining each of said processed left signals and each of saidprocessed right signals; and outputting said combined processed leftsignal and said combined processed right signal using speakers having anarrow geometry.
 13. The method of claim 12 wherein said positionalinformation includes azimuth information and elevation information. 14.The method of claim 13 wherein said positional information furtherincludes range information.
 15. The method of claim 12 wherein saidspeakers are integrated in a handheld device.